Electronic apparatus



' Feb. 28, 1967' FIGLI VOLTAGE A ACROSS 0 POINTS TURN ON B PULSE TO GATEOF a c. 5

CURRENT C PULSE //v A. G. HUFTON ELECTRONIC APPARATUS Filed NOV. 9, 1964TO DISTRIBUTOR WINDING 32 TURN OFF 0 PULSE T0 GATE OF G. C S (TURN OFFVOLHIGEI VOLTAGE E ACROSS WINDING 37 *V DEGREES OF DISTRIBUTOR SHAFTROTATION lnve nror ARTHUR G. HUFTON ATTYS.

United States Patent 3,306,275 ELECTRONIC APPARATUS Arthur G. Hufton,Villa Park, 111., assignor to Motorola, Inc., Franklin Park, Ill., acorporation of Illinois Filed Nov. 9, 1964, Ser. No. 409,793 5 Claims.(Cl. 123148) This invention relates to ignition systems for internalcombustion engines, and more particularly to an improved ignition systemutilizing the capacitor discharge principle.

Capacitor discharge ignition systems, that is, those systems whichutilize a capacitor for intermittently discharg ing and causing currentflow through an ignition coil, have been proposed over a long period oftime. Such ignition systems have been recognized as theoreticallysuperior to other types of ignition systems, but as a practical matter,capacitor discharge systems have not been satisfactory. Many of thecapacitor discharge systems proposed to date have been complex and haverequired a large number of components. Often such systems failed toproduce adequate voltage under certain conditions, and were unstableover variations in ambient temperature.

Accordingly, it is an object of this invention to provide an improved,low cost, ignition system for an internal combustion engine.

Another object of the invention is to provide a capacitor dischargesystem which provides adequate firing voltage for all conditions, andaffords stability at high ambient temperature.

Still another object of the invention is to provide an improved ignitionsystem utilizing the capacitor discharge principle and which is simpleof operation and requires few components.

A feature of the invention is the provision of a firing circuit for anignition coil, which circuit includes a capacitor connected to theignition coil, a circuit for charging the capacitor, and a gatecontrolled semiconductor switch for discharging the capacitor in timedrelation with the internal combustion engine.

Another feature of the invention is the provision, in a capacitivedischarge ignition system, of a transformer having a primary windingconnected in series between a source of potential and a gate controlledsemiconductor switch and having a secondary winding connected to thegate of the semiconductor switch and responsive to current flow in theprimary winding subsequent to discharge of an ignition capacitor toapply a turn off pulse to the gate.

Still another feature of the invention is the provision of a capacitordischarge ignition system having a transformer as above described andwhich includes a further secondary winding connected to the ignitioncapacitor for charging the same by a reverse transient pulse upon turnoff of the semiconductor switch.

In the drawing:

FIG. 1 is a schematic diagram of an igntion system constructed inaccordance with the invention; and

FIG. 2 is a set of curves illustrating the operation of the system wtihrespect to time in degrees of crank shaft revolution.

In accordance with the invention, an ignition system for an internalcombustion engine includes an ignition coil for supplying high voltagefiring pulses to the internal combustion engine and further includespulse means operable in synchronism wtih the internal combustion engine.The ignition system also includes a capacitor and a gate controlledsemiconductor switch connected in series with the ignition coil. Thegate controlled switch is turned on and off at predetermined times topermit 'ice the capacitor, which has been charged to a high voltage, todischarge through the ignition coil and produce firing pulses therein.

A transformer having a primary and two secondary windings is utilized tocontrol the operation of the firing circuit. The primary winding of thetransformer is connected in series between the semiconductor switch andthesource of potential. One of the secondary windings is connected tothe gate region of the semiconductor switch and is responsive to currentflow in the primary winding subsequent to discharge of the capacitor toapply a pluse to the gate region to turn the semiconductor switch off.The other secondary winding is connected to the capacitor and chargesthe capacitor by a reverse transient pulse upon turn off of thesemiconductor switch.

Referring now to FIG. 1, an ignition transformer 11 has a secondarywinding 12 coupled to the center post of a distributor for an internalcombustion engine, not shown, as is well known in the art. Secondarywinding 12 is connected to one end of primary winding 13 which, in turn,is connected to one side of an ignition capacitor 14. The other end ofprimary winding 13 is grounded. Capacitor 14 is connected to the anodeof a gate controlled semiconductor switch 16. Gate controlledsemiconductor switch 16 is of the four layer type and has a gate region17 responsive to pulses of opposite polarity applied thereto to renderthe semiconductor switch 16 conductive and non-conductive respectively.When semiconductor switch 16 is conductive, a circuit path is completedthrough the series combination of the primary winding 13 of transformer11, capacitor 14 and semiconductor switch 16. A protective diode 15 isconnected across semiconductor switch 16 to protect the switch frombackswing voltages in winding 13.

Positive pulses are applied to the control region or gate 17 ofsemiconductor switch 16 by means of a pulse circuit. This pulse circuitis comprised of a pair of breaker points 18 connected in series with theprimary winding 19 of a transformer 20, and through resistor 21 andignition switch 22 to a source of direct current potential, storagebattery 23. Breaker points 18 open and close in synchronism with theoperation of the internal combustion engine, as is well known in theart. Transformer 20 includes a secondary winding 24 which is connectedthrough a resistor 25 to gate region 17 of semiconductor switch 16.

Assuming for the present that a charge is placed on ignition capacitor14 at the proper times, with breaker points 18 closed, current flowlimited by resistor 21 occurs in primary winding 19 of transformer 20.Transformer 20 is wound such that this current produces a negativepotential at the resistor end of secondary winding 24, which has noeffect on semiconductor switch 16. When the points 18 open, however, thecollapsing field in primary winding 19 produces a positive pulse insecondary winding 24, which is applied through resistor 25 to gate 17 ofsemiconductor switch 16. This positive pulse causes semiconductor switch16 to turn on so that capacitor 14 is connected across winding 13.

Almost the full voltage across the ignition capacitor 14 is thus appliedacross primary winding 13 of ignition coil 11 in a very short time,causing a rapid build-up of current. This action induces high voltage inthe secondary winding 12 of ignition coil 11 according to the turnsratio of the ignition coil. This high voltage pulse is then applied tothe center post of the distributor for firing the fuel mixture in therespective cylinders of the internal combustion engine. The breakerpoints 18 shown in the pulsing circuit are merely an example of onepulsing device. Other systems for producing a positive pulse forapplication to transformer 20 for developing a timely output voltage insecondary winding 24 might alsobe utilized within the scope of thisinvention.

Semiconductor switch 16 is turned off by the application of a negativepulse to gate 17. This pulse is developed by means of transformer 31,which has a primary winding 32 connected in series between the storagebattery 23 and the semiconductor switch 16 through diode 33. A capacitor34 is connected across primary winding 32 of transformer 31. Transformer31 further includes a secondary winding 35 which is connected in serieswith a diode 36 across resistor 25. When capacitor 14 has dischargedthrough semiconductor switch 16, this switch will remain conductiveresulting in a rising current pulse in primary winding 32, asillustrated in FIG. 2, curve C. This rising current pulse induces avoltage in secondary winding 35 such that the juncture between winding35 and resistor goes negative. This voltage, illustrated in curve D ofFIG. 2, is applied to the gate electrode 17 of semiconductor switch 16.As may be seen from curve D, when this negative going pulse exceeds theturn off voltage level for the semiconductor switch 16, the switch willbe turned off, reducing primary current and hence the secondary voltage,quickly to zero.

, The energy stored in transformer 31 is also utilized to charge thecapacitor 14. Transformer 31 is provided with a further secondarywinding 37, which is connected in series with a diode 38 across ignitioncapacitor 14. As may be seen from curve E of FIG. 2, when semiconductorswitch 16 is turned off causing the primary current of transformer 31 togo quickly to zero, a voltage backswirig will occur in secondary winding37. This backswing voltage is utilized to charge capacitor 14 throughdiode 38. The backswing voltage appearing in winding is prevented fromtriggering the semiconductor switch 16 by the diode 36. It should benoted that the entire sequence of the operation of the circuit istriggered by a single pulse. Thi permits a wide choice in triggeringmethods utilized. The system is capable of giving a. satisfactory highvoltage output to the spark plugs of an internal combustion engine withall the advantages of capacitor discharge ignition systems, but withfewer components than prior systems. This enables simplicity of designand compactness with greater stability at higher temperatures.

It may therefore be seen that the invention provides an improved lowcost ignition system for an internal combustion engine, which systemutilizes the capacitor discharge principle. The system provides adequatefiring voltages while utilizing a minimum of power and few components.

I claim:

1. In an ignition system for an internal combustion engine, which systemhas an ignition coil for supplying high voltage firing pulses to theinternal combustion engine and pulse means operable in synchronism withthe internal combustion engine, a firing circuit for providingintermittent current flow in the ignition coil to produce firing pulsestherein, including in combination, capacitor -means, charging meanscoupled to said capacitor means for applying a voltage thereto forcharging said capacitor means, a gate controlled semiconductor switchconnected in series with said capacitor means and the ignition coil,said semiconductor switch having a gate region responsive to a pulse ofa given polarity to turn said semiconductor switch on and responsive toa pulse of opposite polarity to turn said semiconductor switch off,means coupled to the pulse means to apply pulses of the given polarityto said gate region to turn said semiconductor switch on and dischargesaid capacitor means through said ignition coil IfOI' producing a firingpulse therein, a transformer having primary and secondary windings, saidprimary winding being connected in series between said semiconductorswitch and a source of potential, said secondary winding being connectedto said gate region and being responsive to current fiow in said primarywinding subsequent to discharge of said capacitor means to apply a pulseopposite said given polarity to said gate region to turn saidsemiconductor switch off.

2. In an ignition system for an internal combustion engine which systemhas an ignition coil for supplying high voltage firing pulses to theinternal combustion engine and pulse means operable in synchronism withthe internal combustion engine, a firing circuit for providingintermittent current fiow in the ignition coil to produce firing pulsestherein, including in combination, capacitor means, a gate controlledsemiconductor switch connected in series with said capacitor means andthe ignition coil, said semiconductor switch having a gate regionresponsive to a pulse of a given polarity to turn said semiconductorswitch on and responsive to a pulse opposite the given polarity to turnsaid semiconductor switch oif, means coupled to said gate region andresponsive to said pulse means to apply pulses of the given polaritythereto in synchronism with the pulse means, a transformer having aprimary winding and first and second secondary windings, said primarywinding being connected in series between said semiconductor switch anda source of potential, said first secondary winding being connected tosaid gate region and being responsive to current flow in said primarywinding subsequent to discharge of said capacitor means to apply a pulseopposite said given polarity to said gate region to turn saidsemiconductor switch off, and means including said second secondarywinding being connected to said capacitor means for charging the same bya reverse transient pulse induced in said second secondary winding uponturn off of said semiconductor switch.

3. In an ignition system. for an internal combustion engine, whichsystem has an ignition coil for supplying high voltage firing pulses tothe internal combustion engine and a source of direct current potential,a firing circuit for providing intermittent current flow in the ignitioncoil to produce firing :pulses therein, including in combination,capacitor means, a gate controlled semiconductor switch connected inseries with said capacitor means and the ignition coil, saidsemiconductor switch having a gate region responsive to a pulse of agiven polarity to turn said semiconductor switch on and responsive to apulse of polarity opposite to the given polarity to turn saidsemiconductor switch oif, means coupled to said gate region to applypulses of the given polarity thereto in synchronism with operation ofthe internal combustion engine, a transformer having a primary windingand a secondary winding, said primary winding being connected in serieswith said semiconductor switch across the source of potential, saidsecondary winding being connected to said gate region and beingresponsive to current flow in said primary winding subsequent todischarge of said capacitor means to apply a pulse of said oppositepolarity to said gate region to turn said semiconductor switch off, andmeans coupled to said transformer and to said capacitor for chargingsaid capacitor by a voltage developed in said transformer in response toturn off of said semiconductor switch.

4. In an ignition system for an internal combustion engine, which systemhas an ignition coil for supplying high voltage firing pulses to theinternal combustion engine and a source of direct current potential, afiring circuit for providing intermittent current flow in the ignitioncoil to produce firing pulses therein, including in combination,capacitor means, a gate controlled semiconductor switch connected inseries with said capacitor means and the ignition coil, saidsemiconductor switch having a gate region responsive to a pulse of agiven polarity to turn said semiconductor switch on and responsive to apulse of polarity opposite to said given polarity to turn saidsemiconductor switch off, means coupled to said gate region for applyingpulses of the given polarity thereto in synchronism with the internalcombustion engine, a transformer having a primary winding and first andsec-- 0nd secondary windings, first rectifier means connecting saidprimary winding in series with said semiconductor switch across a sourceof potential, said first secondary winding being connected to said gateregion and being responsive to current flow in said primary windingsubsequent to discharge of said capacitor means to apply a pulse of theopposite polarity to said gate region to turn said semiconductor switchoh, and second rectifier means connected in series with said secondsecondary Winding across said capacitor means for charging the same by areverse transient pulse induced in said second secondary winding uponturn ofi? of said semiconductor switch.

5. In an ignition system for an internal combustion engine, which systemhas an ignition coil for supplying high voltage firing pulses to theinternal combustion engine and a source of direct current potential, afiring circuit for providing intermittent current flow in the ignitioncoil to produce firing pulses therein, including in combination,capacitor means, charging means coupled to said capacitor means [forapplying a voltage thereto for charging said capacitor means,discharging means coupled to said capacitor means for discharging saidcapacitor means through the ignition coil, a single gate controlledsemiconductor switch included in both said charging and dischargingmeans, said semiconductor switch having a gate region responsive to apulse of a given polarity to turn said semiconductor switch on andresponsive to a pulse of polarity opposite to the given polarity to turnsaid semiconductor switch off, and means coupled to said gate region toapply pulses of a given polarity thereto in synchronism with operationof the internal combustion engine for turning said semiconductor switchon to actuate said discharging means, said charging means including atransformer having a primary win-ding and a secondary winding, saidprimary winding being connected in series with said semiconductor switchacross the source of direct current potential to apply energy to saidtransformer, said secondary winding being connected to said gate regionand applying a pulse thereto to turn oif said semiconductor switch sothat energy in said transformer provides a voltage for charging saidcapacitor.

References Cited by the Examiner UNITED STATES PATENTS 3,049,642 8/1962Quinn 123-148 3,150,286 9/1964 Quinn 123148 3,184,653 5/1965 Hutson.3,219,877 11/1965 Konopa.

References Cited by the Applicant UNITED STATES PATENTS 2,977,506 3/1961Short et al. 3,045,148 7/1962 McNulty et al. 3,078,391 2/ 1963 Bunodiereet al.

MARK NEWMAN, Primary Examiner. LAURENCE M. GOODRIDGE, Examiner,

1. IN AN IGNITION SYSTEM FOR AN INTERNAL COMBUSTION ENGINE, WHICH SYSTEMHAS AN IGNITION COIL FOR SUPPLYING HIGH VOLTAGE FIRING PULSES TO THEINTERNAL COMBUSTION ENGINE AND PULSE MEANS OPERABLE IN SYNCHRONISM WITHTHE INTERNAL COMBUSTION ENGINE, A FIRING CIRCUIT FOR PROVIDINGINTERMITTENT CURRENT FLOW IN THE IGNITION COIL TO PRODUCE FIRING PULSESTHEREIN, INCLUDING IN COMBINATION, CAPACITOR MEANS, CHARGING MEANSCOUPLED TO SAID CAPACITOR MEANS FOR APPLYING A VOLTAGE THERETO FORCHARGING SAID CAPACITOR MEANS, A GATE CONTROLLED SEMICONDUCTOR SWITCHCONNECTED IN SERIES WITH SAID CAPACITOR MEANS AND THE IGNITION COIL,SAID SEMICONDUCTOR SWITCH HAVING A GATE REGION RESPONSIVE TO A PULSE OFA GIVEN POLARITY TO TURN SAID SEMICONDUCTOR SWITCH ON AND RESPONSIVE TOA PULSE OF OPPOSITE POLARITY TO TURN SAID SEMICONDUCTOR SWITCH OFF,MEANS COUPLED TO THE PULSE MEANS TO APPLY PULSES OF THE GIVEN POLARITYTO SAID GATE REGION TO TURN SAID SEMICONDUCTOR SWITCH ON AND DISCHARGESAID CAPACITOR MEANS THROUGH SAID IGNITION COIL FOR PRODUCING A FIRINGPULSE THEREIN, A TRANSFORMER HAVING PRIMARY AND SECONDARY WINDINGS, SAIDPRIMARY WINDING BEING CONNECTED IN SERIES BETWEEN SAID SEMICONDUCTORSWITCH AND A SOURCE OF POTENTIAL, SAID SECONDARY WINDING BEING CONNECTEDTO SAID GATE REGION AND BEING RESPONSIVE TO CURRENT FLOW IN SAID PRIMARYWINDING SUBSEQUENT TO DISCHARGE OF SAID CAPACITOR MEANS TO APPLY A PULSEOPPOSITE SAID GIVEN POLARITY TO SAID GATE REGION TO TURN SAIDSEMICONDUCTOR SWITCH OFF.